Field of the Invention
The present invention relates to condensation and frost control systems and more particularly to a system for use with cooler and freezer entry doors.
The increase in demand for perishable food and other sensitive products have generated large processing, storage and distribution facilities, including low temperature areas with doors opening to unconditioned areas or ambient outdoor environments. Particularly, access to these areas is by means of doors, airlocks or moisture barriers in order to prevent loss of cool air to the exterior and infiltration of warm moist air into the cooler or freezer.
The door systems used with such facilities particularly are designed to be opened easily and rapidly to limit mixture of low temperature air from the interior of the facility with high temperature high humidity air from the outside. Such doors include folding doors which are drawn laterally, swinging doors, plastic strip curtains, vertical sliding horizontal roll, or vertical roll up doors, and high-speed doors.
One problem which has been encountered with all of these doors is the condensation of water and formation of frost or fogging which occurs on the doors, frames and adjacent floors and walls. The condensation drips onto the floor where below freezing surface temperatures transform the water into ice, creating a hazardous condition for workers. Frost and ice build-up on transparent door panels or windows also obstructs vision, creating an additional safety hazard for workers while frost and ice build-up on the frames of the doors may restrict movement and damage the desired uniform barriers separating the low temperature and high temperature areas.
Present technologies for preventing condensation and frost in such applications use heaters to elevate the air temperature around the door and frame. Such systems include those which use radiant heaters mounted above the door opening. One such system is shown for example in U.S. Pat. No. 4,950,869. Other systems utilize blowers in which air is directed over a heating element before being directed onto the door such as is shown in U.S. Pat. No. 5,329,781. These systems attempt to use the warm air to evaporate condensation into vapor. The difficulty with these systems are that radiant heaters cover only a limited portion of the door and frame when mounted above the door opening, while in both systems warm air put on the doors converts frost to water which then drips onto the floor. That water then flows into the low temperature space and freezes into ice continuing to create a hazardous condition, and potentially blocking movement of the door. Moreover, because door openings vary in size, larger doors are not fully treated with either of these systems to prevent condensation of frost. When larger blowers are used to apply warm air to the doors, the warm air tends to move upwardly through convection away from the critical areas of frost build-up at the bottom of the door and on the floor. Accordingly, those prior art systems which rely on warm air have not effectively addressed the problems of condensation and frost.
It is an object of the present invention to control condensation and frost on freezer and cold storage doors.
Another object of the present invention is to control condensation and frost on cooler and freezer doors by using desiccant dehumidification to cause evaporation and sublimation of frost and prevent the appearance of liquid water.
Yet another object of the present invention is to provide a condensation and frost control system for cooler and freezer doors which is economical to manufacture and reliable in use.